Hermann von Helmholtz (1821–1894)

Hermann von Helmholtz (1821-1894) Hermann von Helmholtz died on 8 September a century ago. The occasion has been marked by a major assessment of his scientific life—Hermann von Helmholtz and the Foundations of Nineteenth-Century Science (Cahan 1994). In 1921 the Optical Society of America commissioned the translation of his Handbuch der physiologischen Optik into English (Helmholtz 1924, 1925) to mark the centenary of his birth. Figure 1 portrays Helmholtz enclosed within a diagram of the eye taken from the Handbuch', the original portrait was engraved in 1867, the year in which the Handbuch was published in its entirety. This editorial is a selective survey of some of Helmholtz's work in perception and it focuses on his Optik.